In recent years, there is a growing demand for a discrete semiconductor i.e. a single-function semiconductor device with a standardized specification, unlike a complicated semiconductor device such as an IC and LSI) such as a capacitor, a transistor, a diode, a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) and an IGBT (Insulated Gate Bipolar Transistor). The discrete semiconductor uses a board of a low-resistivity silicon wafer. A silicon monocrystal with a resistivity as low as 20 mΩ·cm or less has come to be demanded as a material of the silicon wafer. An example of the low-resistivity silicon monocrystal is a silicon monocrystal with n-type electrical characteristics highly densely doped with a volatile dopant (e.g. arsenic, red phosphorus and antimony).
The silicon monocrystal is usually manufactured through Czochralski process (referred to as CZ process hereinafter). In order to grow a silicon monocrystal through the CZ process, it has been disclosed that a pulling-up apparatus including a cooler is used to pull up the silicon monocrystal to provide a predetermined temperature gradient (see Patent Literature 1: JP-A-2011-105526). According to Patent Literature 1, a fault-free silicon monocrystal (i.e. a monocrystal without OSF (Oxidation Induced Stacking Fault) and grown-in fault over the entire radial region) can be stably grown at a high yield rate.
However, when the above-described low-resistivity silicon monocrystal for a discrete semiconductor is manufactured using the pulling-up apparatus provided with the cooler as disclosed in Patent Literature 1, a dislocation occurs at a shoulder of the silicon monocrystal.
In order to restrain the dislocation from occurring at the shoulder of the low-resistivity silicon monocrystal, it has been disclosed to control a crystal rotation speed and crucible rotation speed when the shoulder of the monocrystal is formed by the pulling-up (see Patent Literature 2: JP-A-2012-250859). According to Patent Literature 2, since the silicon melt immediately below the crystal is efficiently stirred, the dopant in the silicon melt is diffused to improve an in-plane uniformity of the dopant in the crystal, thereby restraining the dislocation at the shoulder.
When a large-diameter (e.g. 200 mm or more) silicon monocrystal is to be pulled-up, the volume of the crucible has to be increased. In this case, a convection of the silicon melt in the crucible becomes more vigorous, so that the quality of the obtained silicon monocrystal is deteriorated. Accordingly, it is necessary to apply a magnetic field to the silicon melt to restrain the natural convection of the silicon melt in the crucible.
However, Patent Literature 2 is directed to a method in which the monocrystal is pulled up while the monocrystal and the crucible are rotated at a predetermined rotation speed. Even when the natural convection of the silicon melt is restrained by applying the magnetic field to the silicon melt, since the convection of the silicon melt inevitably occurs, the method disclosed in Patent Literature 2 is not suitable for pulling up a large-diameter low-resistivity silicon monocrystal.